CN102664054B - X-ray absorption grate manufacturing method and filling device thereof - Google Patents

Abstract

The invention discloses a manufacturing method of an X-ray absorption grating and a filling device thereof. The manufacturing method is as follows: first depositing a Si3N4 thin film on the surface of a silicon chip and performing photolithography, and making a transparent electrode on the other surface of the silicon chip; The V-shaped groove is obtained by etching the base; a groove with a high aspect ratio and a steep structure is etched on the V-shaped groove; the surface of the silicon base and the inner wall of the groove are modified; the silicon base is immersed in molten heavy metal to fill it under vacuum That is, the X-ray absorption grating is obtained. The filling device includes a sealed furnace body, a vacuuming mechanism and an inflating mechanism; a filling pool, a heating mechanism, a lifting mechanism, and a supporting mechanism are arranged in the sealed furnace body, and an exhaust nozzle is provided on the sealed furnace body, and the exhaust nozzle is connected to the vacuum mechanism. The sealed furnace body is provided with an inflation nozzle and a gas discharge nozzle, and the inflation nozzle is connected with an inflation mechanism. The invention has simple steps, is easy to realize in ordinary laboratories, and can manufacture gratings of any area, and the filling device can fill the silicon base with high quality.

Description

Manufacturing method and filling device of X-ray absorption grating

technical field

The invention relates to a method for making a grating, in particular to a method for making an X-ray absorption grating. The invention also relates to grating manufacturing equipment, in particular to a filling device for metal filling in X-ray absorption grating manufacturing.

Background technique

The X-ray absorption grating is mainly used in the X-ray phase contrast imaging system based on the grating, and is one of the core devices of the system. The X-ray phase contrast imaging system is different from the traditional X-ray absorption imaging system commonly used at present. It is a new imaging method that uses the phase change produced by the X-ray passing through the object to image the object. In fact, substances composed of light atoms have a small absorption factor for X-rays, but a large phase factor, so it is easier to obtain high-quality images of the interior of such substances by using phase contrast than absorption contrast. Therefore, X-ray phase contrast imaging technology has incomparable advantages over traditional X-ray absorption imaging technology. It can be mainly used in the detection of organic materials and devices, biology and medicine, industrial non-destructive testing, gunpowder filling detection and other fields.

In the grating-based X-ray phase-contrast imaging system, the X-ray absorption grating needs to be placed behind the X-ray source, and the heavy metal part of the X-ray absorption grating absorbs X-rays, while the other part of the grating transmits X-rays, so that the absorption The grating and the ordinary desktop X-ray source together constitute an X-ray source with one-dimensional spatial coherence. Each line source has spatial coherence, and there is no coherence between line sources. After reasonable design, the phase contrast images formed by each line source can achieve intensity superposition, so that the X-ray phase contrast imaging system is more efficient. In addition, another X-ray absorption grating is placed at the Taber distance behind the phase grating in the system, which converts object information into Moiré fringe information behind the absorption grating, greatly reducing the difficulty of detection.

The current manufacturing method for X-ray absorption gratings is mainly LIGA technology (the German words Lithographie, Galvanoformung and Abformung, namely the abbreviation of lithography, electroforming and injection molding). LIGA technology is an X-ray lithography technology based on synchrotron radiation sources, which mainly includes three process steps: X-ray synchrotron radiation lithography, electroforming molding and injection molding replication. It draws lessons from the standard IC photolithography process, and has unparalleled advantages in the production of patterns with high aspect ratios, which promotes the development of the field of micromachining. At present, the research units of X-ray phase contrast imaging technology in Switzerland and Japan are using this technology to make X-ray absorption gratings, but so far, the area of X-ray absorption gratings obtained by using this technology is limited. With the development of X-ray phase contrast imaging system technology Mature, it is very likely to be put into practical application in the near future, and at the same time, it will face the demand for imaging with a larger area. Therefore, it is necessary to develop a larger-area X-ray absorption grating, but the current fabrication method cannot realize a large-area X-ray absorption grating production. On the other hand, the current LIGA technology cannot get rid of the limitation of synchrotron radiation sources, that is, the cost of X-ray absorption gratings fabricated by LIGA technology is very high. This restricts the popularization and application of the X-ray phase contrast imaging system.

Contents of the invention

The technical problem to be solved by the present invention is to provide an X-ray absorption grating with simple process steps, easy to realize in ordinary laboratories, and capable of producing X-ray gratings of any area in view of the defects of limited area and high manufacturing cost of the X-ray absorption grating produced in the existing LIGA technology. A method for fabricating an X-ray absorption grating of the absorption grating.

The further technical problem to be solved by the present invention is to provide a heavy metal filling device for X-ray absorption grating production that is easy to operate and capable of filling silicon-based structures with high-quality X-ray strong absorption heavy metals.

The technical solution adopted by the present invention to solve its technical problems is:

A method of manufacturing an X-ray absorption grating, comprising the following steps:

(1) Silicon-based production: select n-type or p-type silicon wafers and make a grating mask, deposit a layer of Si ₃ N ₄ film on either surface of the silicon wafer, and coat the Si ₃ N ₄ film Cover the photoresist, photolithographically print the pattern of the grating mask on the photoresist, remove the Si ₃ N ₄ film at the specified position of the grating mask after developing and fixing, and then remove the photoresist; The other surface is also made of transparent electrodes by photolithography to obtain a silicon base;

(2) Etch V-shaped grooves on the silicon substrate: protect the transparent electrode, use an alkaline etching solution to anisotropically etch the silicon substrate, etch the surface of the silicon substrate that is not covered with Si ₃ N ₄ in step (1). V-shaped groove;

(3) Etching trenches with high aspect ratio and steep structures: using photo-assisted electrochemical etching method to etch trenches with high aspect ratio and steep structures on the basis of the V-shaped grooves formed in step (2) ;

(4) Silicon-based surface modification: modifying the silicon-based surface and the inner wall surface of the groove obtained in step (3) to obtain a layer of modified film;

(5) X-ray strong absorption heavy metal filling: Under vacuum conditions, immerse the silicon base obtained in step (4) into the molten X-ray strong absorption heavy metal, pressurize to fill the groove with the heavy metal, and the filling is completed. X-ray absorption grating.

The manufacturing method of the X-ray absorption grating, in the step (1), includes the following sub-steps:

(11) Make the grating mask of the required pattern according to the X-ray absorption grating; and make the electrode mask of the transparent electrode;

(12) Select an n-type or p-type silicon wafer with a suitable resistivity for polishing and cleaning pretreatment, and then deposit a layer of Si ₃ N ₄ thin film on either surface of the silicon wafer;

(13) Coat a layer of photoresist on the Si ₃ N ₄ thin film, use the prepared grating mask to photoetch the silicon wafer, photoresist the pattern of the grating mask onto the photoresist, and develop , Fixing, using reactive ion etching to remove the Si ₃ N ₄ film at the specified part of the grating mask, and finally remove the photoresist and clean the silicon wafer;

(14) On the other side of the silicon wafer, uniformly deposit a layer of metal as an electrode, coat a layer of photoresist on the surface of the metal, carry out photolithography through the electrode mask, and photolithography the pattern of the electrode mask On the photoresist, after developing and fixing, the corresponding metal is etched away, and the photoresist is removed to obtain a transparent electrode.

The manufacturing method of the X-ray absorption grating, in the step (2), includes the following sub-steps:

(21) Preparation of alkaline etching solution: use alkali metal hydroxide to prepare an aqueous solution with a concentration of 1%-25% by mass as an alkaline etching solution, or use phenyltrimethylammonium hydroxide Alkaline etching solution;

(22) Protect the transparent electrode: install a protective cover resistant to etching solution corrosion outside the transparent electrode to protect the transparent electrode;

(23) Etching V-shaped grooves: first heat up the prepared alkaline etching solution to 50°C-95°C, then put the silicon base into the alkaline etching solution to obtain silicon with V-shaped grooves base.

In the manufacturing method of the X-ray absorption grating, in the step (3), the photo-assisted electrochemical etching is: fixing the silicon substrate with the V-shaped groove formed in the step (2) to the etching On the container, and the side with the V-shaped groove in the silicon base is in contact with the etching solution, and the light in the range of visible spectrum to near infrared spectrum is irradiated on the silicon base through the transparent electrode, and the transparent electrode of the silicon base is used as an anode. A platinum mesh used as a cathode is placed at 1-50mm on the surface of the silicon base with a V-shaped groove, and photo-assisted electrochemical etching is performed on the basis of the V-shaped groove by applying a voltage of 0.5-15V between the cathode and the anode. During the etching process, the temperature of the etching solution is cyclically lowered to keep the temperature of the etching solution constant, and a trench with a high aspect ratio and a steep structure is etched on the silicon substrate.

In the manufacturing method of the X-ray absorption grating, in the step (4), the silicon-based surface modification is to use thermal oxidation method, plasma chemical vapor deposition, anodic oxidation method or sputtering method on the silicon-based surface Carry out oxidation treatment with the inner wall of the trench to form a layer of _SiO2 film as a modified film;

Alternatively, a chemical vapor deposition method is used to grow a Si ₃ N ₄ thin film on the surface of the silicon substrate as a modified thin film.

In the manufacturing method of the X-ray absorption grating, in the step (5), put the silicon base made in the step (4) into the metal filling device, vacuumize the metal filling device and heat the metal filling pool X-ray strong absorption heavy metal until melting, put the silicon base into the molten X-ray strong absorption heavy metal and fill the filling device with nitrogen or inert gas to 1-50 standard atmospheric pressure, and keep it for 5-360min to make X-ray strong absorption The heavy metal enters the groove of the silicon base, and then the silicon base is pulled out of the molten X-ray strong absorption heavy metal liquid surface. After the X-ray strong absorption heavy metal adhered to the silicon base surface drops completely, cool down and release the gas to normal temperature and pressure. , that is, the X-ray absorption grating.

A filling device for filling heavy metals in the manufacture of X-ray absorption gratings, comprising a sealed furnace body with an inner cavity, a vacuum pumping mechanism for pumping air to the sealed furnace body, and an inflating mechanism for inflating the sealed furnace body; The inner cavity of the sealed furnace is provided with a filling pool with a top opening for containing and melting X-ray strong absorption heavy metals, a heating mechanism for heating the filling pool, and a lifting mechanism for moving the silicon base in the inner cavity of the sealed furnace. The lower end of the pulling mechanism is provided with a support mechanism for fixing the silicon base, and the sealed furnace body is provided with an air extraction nozzle communicating with the inner cavity of the sealed furnace, and the air extraction nozzle is connected to the vacuum pumping mechanism, and the sealed furnace body The body is provided with an inflation nozzle and a deflation nozzle communicating with the inner cavity of the sealed furnace, and the inflation nozzle is connected to the inflation mechanism.

In the filling device for heavy metal filling in the manufacture of X-ray absorption gratings, the heating mechanism includes a first heating element arranged around the filling pool outside the filling pool, a second heating element is arranged above the filling pool, and the first heating element The two heating elements enclose a space for preheating the silicon base and removing heavy metals from the surface of the silicon base above the filling pool.

In the filling device for heavy metal filling in the manufacture of X-ray absorption gratings, the lifting mechanism includes a pull rod and a driving member for driving the pull rod to descend or lift, and the support mechanism is fixed at the lower end of the pull rod.

In the filling device for heavy metal filling in the manufacture of X-ray absorption gratings, the support mechanism includes a silicon-based bracket fixedly connected to the pulling mechanism, and the silicon-based bracket is provided with a fixing device for detachably fixing the silicon base. part, and the fixing part fixes the silicon-based edge on the silicon-based support.

In the manufacturing method of the X-ray absorption grating of the present invention, the processes involved in each step are simple processes, and special high-precision equipment is not required, and the manufacturing method ensures the low cost of the X-ray absorption grating and the phase contrast imaging system. Taking n-type silicon as an example, the pattern of the mask template is copied onto the silicon substrate by photolithography, and the silicon nitride in the corresponding part of the pattern is etched away by reactive ion etching, and then each part of the silicon substrate is etched with an alkaline etching solution. Anisotropic etching forms a V-shaped groove, and the tip of the formed V-shaped groove plays a guiding role in the next step of etching the groove with a high aspect ratio and a steep structure. According to Lehmann's theoretical model, in the absence of light , under the action of an external electric field, the area near the cathode of the silicon wafer forms a space charge area, and the area near the anode forms a field-free area. When light is irradiated, the penetration depth of light in the silicon wafer does not exceed tens of microns. The electron-hole pairs generated by the light are collected by the anode, and the holes are formed by anisotropic corrosion through diffusion and convergence of the electric field. The tip (that is, the tip of the V-shaped groove) is collected and participates in the electrochemical corrosion process of silicon there. Ideally, no electron-hole pairs are generated in the space charge region, and the holes diffused from the region where electron-hole pairs are generated are received by the strong field region. Therefore, although the side walls of the V-shaped groove are in contact with the etching solution , but because there is no participation of holes, there will be no lateral corrosion, and a trench with a high aspect ratio and a steep structure will be formed. The surface of the steep structure with high aspect ratio and the inner wall of the trench are further surface modified to form a modified film. The main purpose of modifying the surface of the silicon base is to make the filled X-ray strong absorbing heavy metals (such as gold, platinum, lead, bismuth, etc.) X-rays strongly absorb heavy metals into the silicon-based etched high aspect ratio steep structure, which is conducive to denser filling, and this is directly related to the quality of X-ray absorption gratings. In view of the role of the absorption grating in the X-ray phase-contrast imaging system, if a certain area is not filled or filled with gaps, the obtained image will be distorted and the image quality will be reduced. The X-ray absorption grating manufactured by the method of the invention is filled densely and uniformly, and provides a basis for an X-ray phase-contrast imaging system to obtain high-quality images.

The filling device used for heavy metal filling in the manufacture of X-ray absorption gratings of the present invention is a crucial device in the manufacture of X-ray absorption gratings. The main part of the filling device is a sealed furnace body, and the sealed furnace body is connected with a vacuuming mechanism and an inflating mechanism , the inner cavity of the sealed furnace can be evacuated and filled with high-pressure gas to ensure the vacuum in the silicon-based groove so that the high-temperature molten heavy metal in the inner cavity filling pool can be filled smoothly in a simple state. The filling device can also automatically complete the actions such as immersing the silicon base into the filling tank and pulling the silicon base out of the filling tank after filling through the pulling mechanism. The device of the invention can realize the filling of heavy metals in the silicon-based trench, and the filling is uniform and compact, and the whole device has simple structure and convenient operation.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing and embodiment, in the accompanying drawing:

Fig. 1 is the silicon-based electron micrograph of photo-assisted electrochemical etching in step (3) of Example 1 of the present invention;

Fig. 2 is a silicon-based electron microscope photograph after filling metal in step (5) of Example 1 of the present invention;

Fig. 3 is a schematic structural view of the first embodiment of the silicon base in Example 1 of the present invention;

Fig. 4 is a schematic structural view of the second embodiment of the silicon base in Example 1 of the present invention;

Fig. 5 is a schematic structural view of the third embodiment of the silicon base in Example 1 of the present invention;

Fig. 6 is a schematic structural diagram of Embodiment 2 of the present invention.

Detailed ways

In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific implementation manners of the present invention will now be described in detail with reference to the accompanying drawings.

Embodiment 1. A method for manufacturing an X-ray absorption grating, comprising the following steps:

(1) Silicon-based production: select n-type or p-type silicon wafers and make a grating mask, deposit a layer of Si ₃ N ₄ film on either surface of the silicon wafer, and coat the Si ₃ N ₄ film Cover the photoresist, photolithographically print the pattern of the grating mask on the photoresist, remove the Si ₃ N ₄ film at the specified position of the grating mask after developing and fixing, and then remove the photoresist; The other surface also uses photolithography to make a transparent electrode to obtain a silicon base;

(2) Etch V-shaped grooves on the silicon substrate: protect the transparent electrode, use an alkaline etching solution to anisotropically etch the silicon substrate, etch the surface of the silicon substrate that is not covered with Si ₃ N ₄ in step (1). V-shaped grooves; the arrangement of the V-shaped grooves is the same as or opposite to the pattern arrangement of the grating mask.

(3) Etching trenches with high aspect ratio and steep structures: using photo-assisted electrochemical etching method to etch trenches with high aspect ratio and steep structures on the basis of the V-shaped grooves formed in step (2) ; The high aspect ratio structure means that the depth of the groove is much greater than the width of the groove. Generally, the ratio of the depth to the width of the groove is more than 10. Steep means that the side wall of the groove is perpendicular to the surface of the silicon base or is basically perpendicular to the surface of the silicon base.

(4) Silicon-based surface modification: modifying the silicon-based surface and the inner wall surface of the groove obtained in step (3) to obtain a layer of modified film;

(5) X-ray strong absorption heavy metal filling: Under vacuum conditions, immerse the silicon base obtained in step (4) into the molten X-ray strong absorption heavy metal, pressurize to fill the groove with the heavy metal, and the filling is completed. X-ray absorption grating. Heavy metals with strong X-ray absorption refer to heavy metals with relatively low melting points such as gold, platinum, lead, and bismuth.

In the step (1), the following sub-steps are preferably included:

(11) According to the X-ray absorption grating, make a grating mask with a required pattern. The pattern can be a one-dimensional grating structure, or a two-dimensional grating structure, or other structures that are actually required. And make another electrode mask for the transparent electrode;

(12) Select an n-type or p-type silicon wafer with a suitable resistivity for polishing and cleaning pretreatment, in which the surface of the silicon wafer is polished on both sides, and the n-type or p-type silicon wafer is processed according to the semiconductor standard process requirements Cleaning, depositing a layer of Si ₃ N ₄ thin film by chemical vapor deposition method on any surface of silicon wafer, the thickness of Si ₃ N ₄ thin film can be 10nm-1000nm; repeat.

(13) Coat a layer of photoresist on the Si ₃ N ₄ thin film, use the prepared grating mask to photoetch the silicon wafer, photoresist the pattern of the grating mask onto the photoresist, and develop , fixing, using the reactive ion etching (RIE) method to first remove the Si ₃ N ₄ film at the specified position of the grating mask, and finally remove the photoresist and clean the silicon wafer; the reactive ion etching method is an existing process, and will not be discussed here. Let me repeat.

(14) On the other side of the silicon wafer (on the back of the silicon wafer deposited with Si ₃ N ₄ thin film) uniformly deposit a layer of metal as an electrode, and form a layer of metal layer on the silicon wafer. As the metal of the electrode, choose aluminum, Chromium, nickel, alloy or metal composite layer, coat a layer of photoresist on the surface of the metal layer, use the prepared electrode mask to carry out photolithography, the electrode mask selects the electrode mask with high transmittance grid pattern For the membrane plate, the pattern of the electrode mask plate is photoetched onto the photoresist, after developing and fixing, the corresponding metal is etched away, and the photoresist is removed to obtain a transparent electrode.

In the step (2), the following sub-steps are included:

(21) Preparation of alkaline etching solution: use alkali metal hydroxide to prepare an aqueous solution with a concentration of 1%-25% by mass as an alkaline etching solution, or use phenyltrimethylammonium hydroxide Alkaline etching solution; the concentration of alkaline etching solution is prepared according to the area of the structure to be etched. If the etching area is small, a low concentration of alkaline etching solution can be selected, such as 1%, 2%, 5% and other concentrations The solution, and cooperate with the temperature to control the etching speed; if the etching area is large, a high-concentration alkaline etching solution, such as 15%, 20%, 25% and other solutions, can be appropriately selected, and the etching speed can be controlled in conjunction with the temperature , to avoid excessive or endless corrosion.

(22) Protect the transparent electrode: install a protective cover that is resistant to etching solution corrosion outside the transparent electrode to protect the transparent electrode; the protective cover is sealed around the transparent electrode to completely seal the transparent electrode so that the etching solution cannot enter the protective cover Internally erodes the transparent electrode.

(23) Etching V-shaped grooves: first heat up the prepared alkaline etching solution to 50°C-95°C, then put the silicon base into the alkaline etching solution to obtain silicon with V-shaped grooves base. The mass percent concentration of the solution is 1%-25%, or choose TMAH. Different temperatures and different solution concentrations lead to different etching rates. Therefore, different temperature and concentration combinations are used to control the etching rate. The selected data only needs to be within the above temperature and concentration range. In order to ensure the uniformity of the temperature of the alkaline etching solution, a water bath device can be used to keep the temperature of the alkaline etching solution constant.

In the step (3), the photo-assisted electrochemical etching is: the silicon base with V-shaped grooves made in step (2) is fixed on the etching container, and the silicon base has a V-shaped One side of the tank is in contact with the etching solution. The etching solution is composed of an aqueous solution of alcohol and hydrofluoric acid with a concentration of 1%-30%. Light from the visible spectrum to the near-infrared spectrum is irradiated on the silicon substrate through a transparent electrode. The silicon-based transparent electrode is used as the anode, and a platinum mesh for the cathode is placed 1-50mm away from the silicon-based surface with a V-shaped groove, and a voltage of 0.5-15V is applied between the cathode and the anode in the V-shaped groove. On the basis of photo-assisted electrochemical etching, the temperature of the etching solution is cyclically lowered during the etching process to keep the temperature of the etching solution constant, and a trench with a high aspect ratio and a steep structure is etched on the silicon substrate. The photo-assisted electrochemical etching is performed by using a photo-assisted electrochemical etching device, which is a prior art and will not be repeated here.

In the step (4), the silicon-based surface modification is to oxidize the silicon-based surface and the inner wall of the trench by thermal oxidation, plasma chemical vapor deposition, anodic oxidation or sputtering to form a layer As the _SiO2 film of the modified film, the thickness of the _SiO2 film is 20-1000nm;

Alternatively, a chemical vapor deposition method is used to grow a Si ₃ N ₄ film on the surface as a modified film, and the thickness of the Si ₃ N ₄ film is also 20-1000nm.

The thickness of the film has a certain influence on the density of the filling metal. A film with an appropriate thickness can obtain a dense X-ray absorption grating. If the film thickness is not enough, the filling density of the metal will be poor. Therefore, the Si ₃ N ₄ thin film of the present invention preferably has a thickness of 20-1000 nm.

The above-mentioned thermal oxidation method, plasma chemical vapor deposition, anodic oxidation method and sputtering method are all commonly used thin film manufacturing methods, and will not be repeated here.

In the step (5), the silicon substrate produced in the step (4) is put into the metal filling device, the metal filling device is vacuumed, and the filling pool in the metal filling device is heated, and the temperature of the filling pool is raised so that the X-ray strong absorption heavy metals are melted, and X-ray strong absorption heavy metals are metals with lower melting points such as gold, platinum, lead, and bismuth. Put the silicon base into the molten heavy metal and fill the device with nitrogen or inert gas to 1-50 standard atmospheric pressure. The purpose of vacuuming and filling the gas is to prevent the molten metal element from It is oxidized, pressurized, presses and fills the heavy metal in the molten state into the silicon-based groove, in order to fully fill it, pressurize and keep it for 5-360 minutes so that the heavy metal can fully enter the silicon-based groove, after filling the silicon The base pulls out the metal liquid surface of the filling pool, and after the heavy metal adhered to the surface of the silicon base drops completely, the temperature is lowered and the gas is released to normal temperature and pressure, and the X-ray absorption grating is obtained.

The present invention can be used in the manufacture of various X-ray absorption gratings, such as strip gratings, hole gratings, or other types of absorption gratings. The shape of the absorption grating pattern can be a strip grating as shown in Figure 3. The period and duty cycle of the strip grating are not limited. The pattern shown in Figure 4 is a hole-shaped grating. There are no restrictions on the spacing and period of the polygonal holes or other polygonal holes, and gratings arranged at rectangular intervals as shown in FIG. 5 can also be used. The hatched parts shown in the above figures may be the filled heavy metal parts, or the X-ray transparent parts. The manufacturing method of the present invention will be described in detail below by taking the strip groove grating as an example.

The first step: the preparation of the silicon base. First, make a grating mask according to the required pattern, and then select an n-type or p-type silicon wafer with a suitable resistivity. In this embodiment, an n-type silicon wafer is selected, with crystal orientation (100), unlimited area, and double-sided polishing. Then clean the silicon wafer according to the semiconductor standard process, and after drying, deposit a layer of Si ₃ N ₄ film on either side of the two surfaces of the silicon wafer (this side is called the front side) by using LPCVD (low pressure chemical vapor deposition) technology, The thickness can be 300nm. According to the semiconductor process, the glue coating process is carried out, and the silicon wafer is photoetched using the photolithography technology and the prepared grating mask, and the pattern of the mask template is copied to the photoresist, followed by development and fixing. , and then use reactive ion etching (RIE) to remove the Si ₃ N ₄ film at the specified position, and finally remove the photoresist on the surface of the silicon wafer. After the end, the silicon wafer is cleaned. In addition to the above Si ₃ N ₄ film thickness, the Si ₃ N ₄ film can also be any value between 10~1000nm, such as 10nm, 30nm, 100nm, 200nm, 500nm, 650nm, 700nm, 800nm, 950nm, 1000nm, etc.

Similarly, a transparent electrode is fabricated on the other side of the silicon wafer (this side is referred to as the back side). In this embodiment, an aluminum grid-shaped transparent electrode is fabricated. First, a layer of aluminum is evenly deposited on the back of the silicon wafer, and the same process as above is performed: glue coating, exposure, development, fixing, aluminum etching, and glue removal. Finally, a high-transmittance metal grid-shaped aluminum electrode is formed on the back of the silicon wafer. Silicon substrate preparation can be completed by cleaning the silicon wafer. The thickness of the aluminum electrode should keep the voltage of the whole silicon substrate consistent, that is, the voltage drop on the aluminum electrode is very small.

Step 2: Etching V-shaped grooves on the silicon substrate. On the front side of the silicon base, that is, on the surface of the Si ₃ N ₄ film, use an alkaline etching solution such as KOH or TMAH (phenyltrimethylammonium hydroxide solution) to etch the silicon base anisotropically to make a V-shaped groove structure.

After protecting the transparent electrode, put the silicon base into the alkaline solution, and the reaction equation is:

The specific implementation steps are: taking KOH as an example, first use a material that does not react with the KOH solution to make a protective cover for the transparent electrode, and use the protective cover to wrap the transparent electrode to prevent the KOH solution from corroding the transparent electrode. The material used for the protective cover can be selected as PTFE or PVC. First prepare a certain concentration of KOH solution, the solution concentration can be 1%-25%, and the temperature of the solution is raised to 50°C-95°C. In order to ensure the uniformity of the solution temperature, a water bath device can be used to keep the temperature of the alkaline etching solution constant. The temperature used in etching is different, and the concentration of alkaline etching solution is different, so the etching rate is different.

The third step: using photo-assisted electrochemical etching technology to etch a one-dimensional trench structure on the silicon base. Using a photo-assisted electrochemical etching device, the outer barrel of the device is filled with cooling water, and there is a water outlet and a water inlet. They are connected by pipelines and pass through a low-temperature constant temperature bath. Cooling water enters the outer barrel of the device, and the circulation can keep the temperature of the cooling water constant, avoiding the heating of the cooling water caused by light irradiation. On the other hand, cooling water can be used to filter out infrared light above 1100nm, reducing or even avoiding the etching effect of this part of light on silicon wafers. A piece of quartz glass is pasted under the outer barrel, through which the light reaches the silicon chip to maintain the reaction. The reaction chamber is made of polytetrafluoroethylene, and there is a round hole at the bottom. The diameter can be adjusted according to the size of the silicon base. The silicon base is fixed at the round hole at the bottom of the reaction chamber through an O-ring and an aluminum ring. The V-shaped groove is The surface of the silicon base is an etching surface, that is, the front side is placed facing the reaction chamber, and the transparent electrode is located outside the reaction chamber. A filter can be placed under the silicon substrate during the experiment. In the reaction, try to ensure that the liquid level in the reaction chamber is equal to the water level in the outer bucket of the device. The etching solution is composed of an aqueous solution of hydrofluoric acid, an etching solution, and alcohol, a surfactant. The silicon-based transparent electrode is used as an anode, the etched surface is in contact with the etching solution, and a platinum mesh is placed near the silicon-based etched surface, which is used as a cathode. The platinum net is fixed on the shower device, and the entire surface of the platinum net is evenly distributed with small holes with a diameter of 0.5mm. The role of the shower device is to circulate the etching solution to ensure that the part of the etching solution fully in contact with the etching hole of the silicon wafer is kept fresh and free of bubbles. The etching solution is sucked through the acid-resistant pump from the platinum mesh holes of the cathode, and returned to the reaction chamber after being cooled by the low-temperature constant temperature tank to ensure that the temperature in the reaction chamber is stable and the same as the cooling water temperature in the outer barrel. A thermocouple was used to monitor the temperature change of the etching solution in real time. Illumination is provided by a uniformly distributed array of tungsten-halogen lamps. Experimentally, a thyristor is used to control the voltage applied to the tungsten-halogen lamps to adjust the light intensity.

Use photo-assisted electrochemical etching technology to etch steep trenches with high aspect ratio. The etching time is determined according to the concentration of the etching solution and the temperature of the etching solution. The etching current is related to the concentration, temperature and duty cycle of the pattern. Finally determined by the Lehmann formula, J _ps =Cc ^1.5 exp(-E _a /K _B T), where J _ps represents the current density required for mass transport at a specific HF concentration and solution temperature, C=3300A/cm ² , c represents the weight ratio concentration of HF, E _a =0.345eV. At the same time, it is necessary to ensure that the voltage across the silicon base is in the normal etching area. In this way, an etched pattern with a high aspect ratio structure can be obtained. The etching conditions of this embodiment are: the concentration of the etching solution is 5%, the temperature is set to 21°C, the etching current is determined according to the etching area, the groove depth of the high aspect ratio structure shown in Figure 1 is 110 μm, and the period is 42μm, and the duty cycle is 3/4.

Step 4: modifying the surface of the silicon base with a high aspect ratio steep structure to obtain a modified film. Before modification, the surface should be cleaned according to the semiconductor process, and then dried in an oven. The main purpose of the surface modification of the silicon-based microstructure is to make the filled X-ray strong absorbing heavy metals (such as gold, platinum, lead, bismuth, etc.) The molten heavy metals enter the high-aspect-ratio steep structures etched into the silicon base. The modification treatment method adopted includes oxidation treatment or nitriding treatment on the silicon-based microstructure to obtain SiO ₂ thin film or Si ₃ N ₄ thin film respectively. Oxidation treatment mainly adopts thermal oxidation method, including dry oxygen oxidation and wet oxygen oxidation. The oxide film formed by dry oxygen oxidation has a dense, dry and uniform structure, but the oxidation rate is slow. The dry oxygen-wet oxygen-dry oxygen method is mostly used, which not only ensures the oxidation quality, but also solves the problem of growth rate. No matter which oxidation method is used, it is necessary to control the oxidation temperature, oxidation time and heating and cooling rate. In order to achieve a better filling effect, the thickness of the SiO ₂ film is between 20-1000nm. In this embodiment, the thickness of the SiO ₂ film is not less than 50 nm.

There are many ways to grow SiO ₂ thin films, such as ion chemical vapor deposition, anodic oxidation, sputtering and so on.

Nitriding of the silicon-based structure mainly uses chemical vapor deposition to grow a layer of Si ₃ N ₄ film on the surface.

Step 5: X-ray strong absorption heavy metal filling. Put the modified silicon base in the filling device and evacuate the filling device, so that the silicon base is in a vacuum environment, and the vacuum is evacuated to 10pa. The vacuuming time is different for different sizes of microstructures. The smaller the size of the microstructure, the longer the vacuuming time. longer. Then heat the X-ray strong absorption heavy metal to melt, immerse the silicon base into the molten X-ray strong absorption heavy metal, stop vacuuming, fill with nitrogen or inert gas, so that the pressure in the filling device is not lower than 1 atmosphere, to ensure the melting Heavy metals enter the silicon-based trench structure under pressure and reach a certain density. After filling, pull the silicon base out of the metal liquid level of the filling pool, and wait until the heavy metals remaining on the surface drop completely. Then cool down at a certain rate and deflate. When the temperature drops to room temperature, open the furnace door and take out the grating.

In this embodiment, metallic bismuth is used as the filling metal, and the melting point of metallic bismuth is 271.3°C. After filling, the structure shown in Figure 2 is obtained.

Embodiment 2, as shown in Figure 6, is used for the filling device of metal filling in X-ray absorption grating manufacture, comprises the sealing furnace body 1 with inner cavity, the vacuum pumping mechanism 71 that carries out air extraction to sealing furnace body and sealing An inflating mechanism 61 for inflating the furnace body. The inner cavity of the sealed furnace body 1 is provided with a filling pool 2 with a top opening for containing and melting heavy metals, a heating mechanism 3 for heating the filling pool 2, and is used to place the silicon base 100 in the The lifting mechanism 4 that moves in the cavity of the sealed furnace body, the lower end of the lifting mechanism 4 is provided with a support mechanism 5 for fixing the silicon substrate 100, and the sealed furnace body 1 is provided with a connecting rod that communicates with the inner cavity of the sealed furnace body 1 Air extraction pipe mouth 72, described air extraction pipe mouth 72 is connected with vacuum pumping mechanism 71, and described sealed furnace body 1 is provided with the inflatable pipe mouth 62 and deflation pipe mouth 63 that communicate with sealed furnace body 1 inner cavity, described inflatable pipe The port 62 is connected with the inflation mechanism 61 .

The sealed furnace body 1 must have good sealing performance, and the sealing performance must be able to vacuumize to ^{10 -2} Pa. The sealed furnace body 1 is provided with an operation port (not shown in the figure), and the operation port is provided with a A sealed operation door (not shown in the figure), the inner wall of the operation door is provided with a sealing ring for sealing the gap between the operation door and the sealed furnace body 1 . The shape of the sealed furnace body 1 is not limited, as long as it has an inner cavity space for filling the silicon base 100 .

The filling pool 2 set in the sealed furnace body 1 is a cylindrical structure with an opening on the upper part, which is used for the silicon base 100 to enter and exit conveniently. The filling pool 2 is made of high-temperature resistant materials, so it can be used to contain heavy metals that absorb X-rays in a molten state. Such as ceramics, quartz, stainless steel, etc., the shape of the filled pool 2 is not limited, and may be a cuboid structure, a cylinder structure, or other column structures, or an irregular structure. Cuboid, cube and cylinder structures are generally preferred. The size of the filling pool 2 is such that the amount of molten heavy metal in the filling pool 2 can completely submerge the silicon substrate 100 placed therein.

The heating mechanism 3 is used to heat the filling pool 2 and the space above the filling pool 2 for containing and preheating the silicon base, so the heating mechanism 3 includes a first heating element 31 arranged around the filling pool 2 outside the filling pool 2 , a second heating element 32 is arranged above the filling tank 2 . The first heating element 31 heats the filling pool 2, and the heating temperature should reach the melting of the metal in the filling pool 2. The shape of the first heating element 31 is not limited, and may be a filamentary structure, and the first heating element 31 is wound on the outer wall of the filling tank 2 . The first heating element 31 can also be a plate-like structure or a plurality of block-shaped structures, and is arranged outside the filling pool 2 at a close distance. for heating. It is most preferable to heat the surroundings and the bottom surface of the filling pool 2 at the same time, which can ensure the uniformity of heating, and then keep the temperature of the molten metal in the filling pool 2 uniform and constant. The second heating element 32 forms a space above the filling pool 2 for silicon substrate preheating and surface metal removal, corresponding to the top and bottom of the filling pool 2. Before filling, the silicon substrate 100 is preheated in this space. The silicon base 100 is pulled into the space, and the temperature of this space is kept consistent with the temperature of the filling pool 2, so that the metal on the silicon base 100 remains in a liquid state, and the metal liquid remaining on the surface of the silicon base 100 drops back to the filling pool 2, ensure that no metal remains on the surface of the silicon base 100 after filling, so as not to affect the quality of the absorption grating. The second heating element 32 is preferably a plate-shaped or cylindrical structure. In the plate-shaped structure, at least two sides and the top surface form a heating space. The top of the second heating element 32 is provided with an opening for the pull rod 42 in the lifting mechanism 4. passed. In this embodiment, graphite plates are selected for the first heating element 31 and the second heating element 32 . An external power supply 33 is provided outside the sealed furnace body 1 for heating the first heating element 31 and the second heating element 32. The first heating element 31 and the second heating element 32 can use the same external power supply 33, or Each external power supply 33 can be connected separately.

The lifting mechanism 4 includes a pull rod 42 and a driving member 41 for driving the pull rod 42 to descend or lift, and the silicon base 100 supporting mechanism 5 is fixed at the lower end of the pull rod 42 . The pulling mechanism 4 is used to put the silicon base 100 into the filling pool 2, and to extract the filled silicon base 100 from the filling pool 2. The pull rod 42 in the pulling mechanism 4 only needs to be lowered or lifted. Therefore, the pulling mechanism 4 is set above the filling pool 2, preferably directly above the filling pool 2, the pull rod 42 is vertically set, the pull rod 42 drives the support mechanism 5 of the silicon base 100 to move up and down, and puts the silicon base 100 into the molten heavy metal, or The silicon substrate 100 is lifted out of the fill cell 2 . The driving part 41 is the power source of the pull rod 42 , which can be an air cylinder or an oil cylinder, or a motor with a screw mechanism to drive the silicon base 100 supporting mechanism 5 . Since the inside of the sealed furnace body 1 is high temperature, the drive member 41 is arranged outside the sealed furnace body 1, the pull rod 42 can extend through the sealed furnace body 1 into the filling pool 2, and the sealed furnace body 1 and the corresponding second heating element 32 Inserting holes 11 are respectively opened on the top for wearing the pull rods 42, and the inserting holes 11 on the sealed furnace body 1 are provided with seals for sealing the gap between the pull rods 42 and the inserting holes.

The support mechanism 5 for the silicon base 100 includes a bracket 51 fixedly connected to the pulling mechanism 4, and a fixing member 52 for fixing the silicon base 100 is arranged on the bracket 51, and the fixing member 52 fixes the edge of the silicon base 100 on bracket 51. The support 51 is provided with a plane for placing the silicon base 100 , which at least ensures that the surrounding edges of the silicon base 100 are placed on the plane. The support 51 can be a flat plate or a frame. The surface of the flat plate is flat, and at least two sides of the frame form a common plane for supporting the silicon substrate 100 . The support 51 can also be at least two support blocks arranged at even intervals, the support blocks are arranged on the same circumference and fixed together by connecting pieces, and the support blocks form a common plane for supporting the silicon substrate 100 . The support 51 is also provided with a detachable fixing piece 52 for fixing the silicon base 100. The structure of the fixing piece 52 has multiple types. For example, the fixing piece 52 can be provided with a pressing plate or a pressing plate for pressing the silicon base 100 around the silicon base 100. The pressing block, the fixing member 52 may also be a jig that presses the outside of the edge of the silicon substrate 100 . In this embodiment, the fixing member 52 is a clamp, and the clamp includes a first clamping plate 521 and a second clamping plate 522. The first clamping plate 521 is fixed on the plane of the bracket 51 by detachable screws. The first clamping plate 521 And the second clamping plate 522 clamps the edge of the silicon base 100, the first clamping plate 521 and the second clamping plate 522 can clamp all the edges around the silicon base 100, then the first clamping plate 521 and the second clamping plate 522 are in the shape of the edge of the silicon base 100 The same ring can also clamp part of the edge of the silicon base 100. In such a structure, at least one of the first clamping plate 521 and the second clamping plate 522 is composed of at least two parts arranged at intervals, preferably at least two parts are symmetrical about the center line The setting is or is symmetrical about the central axis. For example: the first clamping plate 521 is a circular plate, an annular plate, a square plate or other polygonal plates, and the second clamping plate 522 is an annular plate or a square annular plate matched with the first clamping plate 521 . Or preferably, the first splint 521 is a plurality of arc-shaped plates and strip-shaped plates arranged at intervals.

The air extraction nozzle 72 that is provided with on the wall of the sealed furnace body 1 is connected with a vacuum pumping mechanism 7, and the vacuum pumping mechanism 7 is a vacuum pump. In the inflation nozzle 62 and the deflation nozzle 63 connected with the inner chamber of the sealed furnace body 1, the inflation nozzle 62 is connected with an inflation mechanism 61, and the inflation mechanism 61 is a high-pressure gas cylinder or other high-pressure pipelines, and the high-pressure gas cylinder is filled with nitrogen or Inert gas, vent pipe port 63 Unicom external environment. A barometer 8 is provided on the sealed furnace body 1 for measuring the air pressure in the sealed furnace body 1 .

Claims (10)

1. a method for making for X ray absorption grating, is characterized in that, comprises the following steps:

(1), silica-based making: select N-shaped or p-type silicon chip and make grating mask plate, deposit one deck Si on arbitrary surface on silicon chip two surfaces ₃n ₄film, at Si ₃n ₄on film, apply photoresist, the pattern photoetching of described grating mask plate, to photoresist, is removed to the Si of position, grating mask plate gauge bonding part successively after development, photographic fixing ₃n ₄film, then remove photoresist; Then also obtain silica-based by photoetching making transparency electrode on another surface of silicon chip;

(2), silica-based upper etching V-shaped groove: protect transparency electrode, utilize alkaline etching solution to the silica-based anisotropic etch that carries out, do not cover Si in step (1) ₃n ₄silicon substrate surface etch V-shaped groove;

(3), the groove of the steep structure of etching high-aspect-ratio: utilize light to help the groove that etches the steep structure of high-aspect-ratio on the basis of the V-shaped groove that electrochemical etching method makes in step (2);

(4), silicon substrate surface modification: silicon substrate surface and trench wall face that step (3) is obtained carry out modification, obtain one deck modification film;

(5), X ray absorbs by force heavy metal and fills: under vacuum condition, the X ray of the silica-based immersion fusing that step (4) is obtained absorbs by force in heavy metal, and pressurization makes to fill described heavy metal in groove, and end-of-fill obtains X ray absorption grating.

2. the method for making of X ray absorption grating according to claim 1, is characterized in that, in described step (1), comprises following sub-step:

(11), make the grating mask plate of required pattern according to X ray absorption grating; And separately make the electrode mask plate of transparency electrode;

(12) N-shaped or the p-type silicon chip, selecting to have suitable resistivity do polished and cleaned pre-service, the then arbitrary surface deposition one deck Si in silicon chip two surfaces ₃n ₄film;

(13), at Si ₃n ₄on film, apply one deck photoresist, utilize the grating mask plate of making to carry out photoetching to silicon chip, by the pattern photoetching of grating mask plate, to photoresist, development, photographic fixing, utilize reactive ion etching first to remove the Si of position, grating mask plate gauge bonding part ₃n ₄film, finally removes photoresist cleaning silicon chip;

(14), the metal as electrode at another side uniform deposition one deck of silicon chip, apply one deck photoresist in this metal surface, carry out photoetching by electrode mask plate, by the pattern photoetching of this electrode mask plate to photoresist, after development, photographic fixing, etch away corresponding metal, photoresist is removed and obtained transparency electrode.

3. the method for making of X ray absorption grating according to claim 1, is characterized in that, in described step (2), comprises following sub-step:

(21), prepare alkaline etching solution: select alkali metal hydroxide be made into mass percentage concentration be the aqueous solution of 1%-25% as alkaline etching solution, or select phenyl trimethylammonium hydroxide to make alkaline etching solution;

(22), protection transparency electrode: the protective sleeve that installs resistance to etching solution corrosion in transparency electrode outward additional is protected transparency electrode;

(23), etching V-shaped groove: first the alkaline etching solution preparing is warming up to 50 DEG C-95 DEG C, then puts in alkaline etching solution silica-based, obtain silica-based with V-shaped groove.

4. the method for making of X ray absorption grating according to claim 1, it is characterized in that, in described step (3), described light helps electrochemical etching to be: what step (2) was made is fixed on etching container with the silica-based of V-shaped groove, and the one side with V-shaped groove in silica-based contacts with etching solution, by visible spectrum to the light near infrared spectral range by transparency electrode expose to silica-based on, silica-based transparency electrode is made to anode, place the platinum net for making negative electrode at the silicon substrate surface 1-50mm place near with V-shaped groove, on basis by the voltage applying 0.5-15V between negative electrode and anode at V-shaped groove, carry out light and help electrochemical etching, in etching process, etching solution is carried out to circulation temperature lowering, to keep etching solution temperature constant, etching obtains the groove of the steep structure of high-aspect-ratio on silica-based.

5. the method for making of X ray absorption grating according to claim 1, it is characterized in that, in described step (4), described silicon substrate surface modification is to adopt thermal oxidation method, plasma activated chemical vapour deposition, anodizing or sputtering method to carry out oxidation processes to silicon substrate surface and trench wall, forms the SiO of one deck as modification film ₂film;

Or employing chemical gaseous phase depositing process is the Si as modification film at silicon substrate surface growth one deck ₃n ₄film.

6. the method for making of X ray absorption grating according to claim 1, it is characterized in that, in described step (5), silica-based the putting in metal filled device that step (4) is made, the X ray that metal filled device vacuumizes and heating of metal is filled in pond is absorbed by force to heavy metal to fusing, the silica-based X ray of putting into fusing is absorbed by force in heavy metal and filling device is filled with to nitrogen or inert gas to 1-50 standard atmospheric pressure, keeping 5～360min to make X ray absorb by force heavy metal enters in silica-based groove, then the silica-based X ray that lifts out fusing is absorbed by force to heavy metal liquid level, after the X ray adhering to until silicon substrate surface absorbs by force heavy metal and drips completely, lower the temperature and exit to normal temperature and pressure, obtain X ray absorption grating.

7. make for X ray absorption grating the filling device that heavy metal is filled, it is characterized in that, comprise the vacuum device of bleeding with the sealing body of heater of inner chamber, to sealing body of heater and the inflation mechanism that sealing body of heater is inflated, in described sealing body of heater, be provided with splendid attire and melt X ray the open-topped filling pond that absorbs by force heavy metal, the heating arrangements heating filling pond, be used for the shift mechanism moving silica-based in sealing body of heater, described shift mechanism lower end is provided with for to the silica-based supporting mechanism being fixed, on described sealing body of heater, be provided with the mouth of pipe of bleeding with Sealing furnace intracoelomic cavity UNICOM, the described mouth of pipe of bleeding connects described vacuum device, described sealing body of heater is provided with aerating pipe port and the nosepipe with Sealing furnace intracoelomic cavity UNICOM, described aerating pipe port connects described inflation mechanism.

8. the filling device of making heavy metal filling for X ray absorption grating according to claim 7, it is characterized in that, described heating arrangements is included in fills outside pond around first heating member of filling pond setting, above filling pond, be provided with the second heating member, described the second heating member encloses the space of covering silica-based preheating and the removal of silicon substrate surface heavy metal above described filling pond.

9. the filling device of making heavy metal filling for X ray absorption grating according to claim 7, it is characterized in that, described shift mechanism comprises pull bar and the actuator that drives pull bar to decline or promote, and described supporting mechanism is fixed on described pull bar lower end.

10. the filling device of making heavy metal filling for X ray absorption grating according to claim 7, it is characterized in that, described supporting mechanism comprises the silica-based support being fixedly connected with shift mechanism, on described silica-based support, be provided with the silica-based detachably fixing fixture that carries out, described fixture is fixed on silica-based edge on silica-based support.